This invention relates to a drive apparatus for driving the auxiliary equipment for an engine of an automobile or other vehicle. More particularly, it relates to a drive apparatus which can drive auxiliary equipment at a speed independent of the speed of the engine.
In an engine for an automobile or other vehicle, auxiliary equipment such as alternators, water pumps, air conditioner compressors, and oil pumps for hydraulic steering are belt driven by a drive pulley provided on the end of the crank shaft. This auxiliary equipmemt is generally designed to be operated at speeds which are low compared to the operating speeds of the engine, and if driven at the same speed as the engine when the engine is running at high speeds, the operation of the equipment would produce considerable power losses. Therefore, means are generally provided for adjusting the speed of the drive pulley for the auxiliary equipment with respect to the rotational speed of the engine so that the auxiliary equipment can be operated at suitable speeds.
For example, Japanese Laid-Open Patent Application No. 58-200838 discloses a speed reduction apparatus for engine auxiliary equipment comprising a planetary reduction gear and a unidirectional clutch provided between an engine crank shaft and a pulley for auxiliary equipment, as well as a directly-coupled clutch comprising a hydraulic piston. At low engine speeds, the rotation of the crank shaft is transmitted directly to the pulley via the directly-coupled clutch. When the engine speed reaches a certain level, the directly-coupled clutch is disengaged, and the rotation of the crank shaft is transmitted to the pulley via the planetary reduction gear and the one-way clutch at a reduced speed.
However, there is a sudden change in the speed of the auxiliary equipment when the directly-coupled clutch is engaged or disengaged, which causes a shock to be imparted to both the engine and the auxiliary equipment. This shock reduces the stability of the automobile and imparts an unpleasant sensation to the driver. Furthermore, there are problems with the durability of the planetary gear reduction gear, and these problems can easily cause noise problems to develop. Thus, this apparatus is not practical. Also, as a planetary reduction gear is employed, the reduction ratio is constant.
Japanese Laid Open Utility Model Application No. 58-86434 discloses a variable speed drive apparatus for auxiliary equipment which utilizes two variable pitch pulleys. A variable pitch drive pulley is disposed on a crank shaft and a variable pitch driven pulley which is driven by the drive pulley with a belt is connected to auxiliary equipment which is to be driven. Each pulley comprises a stationary portion and a movable portion which can be moved towards and away from the stationary portion in the axial direction of the pulley by a hydraulic cylinder mounted on the drive pulley so as to change the effective pitch of the pulley, thereby adjusting the degree of reduction provided by the pulleys and controlling the speed of the auxiliary equipment driven by the driven pulley.
However, in this apparatus, a high pressure oil source is necessary to operate the hydraulic cylinder, and the structure of the hydraulic actuator for the hydraulic cylinder is complicated. Furthermore, the apparatus projects by a considerable amount in the axial direction of the crank shaft of the engine, and thus it is not suitable for automobiles having a limited installation space such as front wheel drive automobiles in which the engine is disposed sideways.